Methods and apparatus for securing turbine nozzles

ABSTRACT

A method for assembling a turbine, wherein the method includes coupling at least one nozzle assembly including an outer band, an inner band, a nozzle, and a dovetail, to a stator that includes a plurality of dovetail slots and channels defined therein, slidably coupling the at least one nozzle assembly into a respective dovetail slot, and fixedly securing the at least one nozzle assembly to the stator with a load pin that extends between the nozzle assembly and the dovetail slot.

BACKGROUND OF INVENTION

[0001] This invention relates generally to turbine engine and more particularly, to methods and apparatus for securing turbine nozzles.

[0002] At least some known turbine stator assemblies include a plurality of stationary turbine nozzles that channel flow towards a turbine. More specifically the nozzles are arranged in axially-spaced stages within a turbine stator and each nozzle includes an airfoil vane that extends outwardly from a dovetail that couples the nozzle to a complimentary-shaped slot defined in the stator.

[0003] An overall operating efficiency of a turbine engine is related to the flow dynamics within the turbine, and as such, engine efficiency may be limited by the ability of aerodynamic components to remain in alignment. Moreover, securing aerodynamic components, such as nozzle assemblies, facilitates reducing flow variations and increasing engine efficiency.

[0004] However, during operation, the nozzles may be urged in a tangential direction as steam flows through the nozzle vanes. The loads are transmitted from the nozzles to the stator through the complementary dovetail surfaces. However, overtime the stress loading may loosen the nozzle dovetail with regard to the slot, and as a result, a useful life of the nozzle may be reduced.

SUMMARY OF INVENTION

[0005] In one aspect, a method is provided for assembling a turbine. The method includes coupling at least one nozzle assembly including an outer band, an inner band, a nozzle, and a dovetail, to a stator that includes a plurality of dovetail slots and channels defined therein, slidably coupling the at least one nozzle assembly into a respective dovetail slot, and fixedly securing the at least one nozzle assembly to the stator with a load pin that extends between the nozzle assembly and the dovetail slot.

[0006] In another aspect, a stator assembly for a turbine is provided including a stator that includes a plurality of dovetail slots and channels, at least one nozzle assembly secured to the stator, wherein the at least one nozzle assembly includes an outer band, an inner band, a nozzle, and a dovetail, and wherein the nozzle extends radially outwardly from each dovetail. The stator assembly also includes at least one load pin for securing the at least one nozzle assembly to the stator such that the load pin extends between the at least one nozzle assembly dovetail and the at least one stator dovetail slot.

[0007] In yet another aspect, a turbine is provided that includes at least one rotor assembly, at least one stator assembly in flow communication with the at least one rotor assembly, wherein the at least one stator assembly includes a stator that includes a plurality of dovetail slots and channels. The turbine also includes at least one nozzle assembly that is secured to the stator, wherein the at least one nozzle assembly includes an upstream side, a downstream side, a vane and a dovetail, and wherein the vane extends radially from the dovetail. The turbine further includes at least one load pin for securing the at least one nozzle assembly to the stator such that the load pin extends between the nozzle assembly dovetail and the stator dovetail slot.

BRIEF DESCRIPTION OF DRAWINGS

[0008]FIG. 1 is a partial perspective of an exemplary turbine engine;

[0009]FIG. 2 is an enlarged schematic cross-sectional view of a portion of the turbine engine shown in FIG. 1;

[0010]FIG. 3 is an enlarged cross-sectional side view of a load pin used in the turbine nozzle assembly shown in FIG. 2; and

[0011]FIG. 4 is an end view of the load pin shown in FIG. 3.

DETAILED DESCRIPTION

[0012]FIG. 1 is a partial perspective view of a steam turbine 10 including a rotor assembly 12 and a stator assembly 14. Rotor assembly 12 includes a shaft 16 and a plurality of bucket assemblies 18. Each bucket assemblies 18 include a plurality of buckets 20 arranged in rows extending circumferentially around shaft 16.

[0013] Stator assembly 14 includes a stator 22 and a plurality of nozzle assemblies 28. Nozzle assemblies 28 include a plurality of nozzles 30 arranged in rows extending inward circumferentially around stator 22. Nozzles 30 cooperate with buckets 20 to form a turbine stage and to define a portion of a steam flow path through turbine 10.

[0014] In operation, steam 24 enters an inlet 26 of turbine 10 and is channeled through nozzles 30. Nozzles 30 direct steam 24 downstream against buckets 20. Steam 24 passing through the turbine stages imparts a force on buckets 20 causing shaft 16 to rotate. At least one end of turbine 10 may extend axially away from shaft 16 and may be attached to a load or machinery (not shown), such as, but not limited to, a generator, and/or another turbine. Accordingly, a large steam turbine unit may actually include several turbines that are all co-axially coupled to the same shaft 16. Such a unit may, for example, include a high-pressure turbine coupled to an intermediate-pressure turbine, which is coupled to a low-pressure turbine. In one embodiment, steam turbine 10 is commercially available from General Electric Power Systems, Schenectady, N.Y.

[0015]FIG. 2 is an enlarged schematic cross-sectional view of a portion of turbine engine 10 shown in Figure including rotor assembly 12 and stator assembly 14. Each stator assembly 14 includes a plurality of dovetail slots 32 and channels 33, and at least one radial load pin 34. Dovetail slots 32 are circular or arcuate in configuration when viewed axially and facilitates coupling each nozzle assembly 28 to stator 22. Dovetail slots 32 are defined by a first side slot wall 35 and a second side slot wall 36 and a radially inward slot wall 37. Substantially annular retaining rings 38 extend from each side slot wall 35 and 36. Channels 33 are generally complimentary in shape to load pins 34. In the exemplary embodiment, a pair of channels 33 extend along each inward slot wall 37 configured to receive at least one radial load pin 34.

[0016] Nozzle assemblies 28 include nozzles 30 that each include an airfoil 42 that extends between a radially outer band 44 and a radially inner band 46. Nozzle dovetail 40 extends radially outward from airfoil 42. Airfoil 42 includes a first contoured sidewall 48 and second contoured sidewall 50. First sidewall 48 is convex and defines a suction side of airfoil 42. Second sidewall 50 is concave and defines a pressure side of airfoil 42. Sidewalls 48, 50 are joined at a leading edge 52 and at an axially spaced trailing edge 54 of airfoil 42.

[0017] Nozzle dovetail 40 is generally complimentary in shape to stator dovetail slots 32. Nozzle dovetail 40 includes an upstream side 56 and a downstream side 58. In the exemplary embodiment, upstream side 56 and downstream side 58 are parallel. Nozzle assemblies 28 has a first axial face 60 and an opposite second axial face 62 that each extend between upstream and downstream sides 56, 58. Upstream side 56 includes a side shoulder 64, known as an outer tang, that extends substantially perpendicularly from upstream side 56 and defines an overhang 66. A dovetail tang 68 also extends substantially perpendicularly from the upstream side 56 and is substantially parallel to the side shoulder 64, such that an upstream side slot 70 is defined between dovetail tang 68 and shoulder 64.

[0018] Nozzle assembly downstream side 58 includes a side shoulder 72 that extends substantially perpendicularly from downstream side 58. In an exemplary embodiment, shoulder 72 is substantially co-axially aligned with respect to upstream shoulder 64. Side shoulder 72 defines a downstream side overhang 74. A dovetail tang 76 also extends substantially perpendicularly from the downstream side 58 and is substantially parallel to side shoulder 72, such that a downstream side slot 78 is defined between. In the exemplary embodiment, downstream dovetail tang 76 is substantially co-axially aligned with respect to upstream dovetail tang 68.

[0019] During assembly of stator assembly 14, each respective nozzle assembly 28 is inserted into dovetail slot 32, then circumferentially slid through dovetail slot 32. Nozzle assemblies 28 are then secured to stator 22 by inserting at least one radial load pin 34 into at least one channel 33. Additional nozzle assemblies 28 are then slidably coupled to stator assembly 14 in a similar fashion about stator 22.

[0020] Load pin 34 is substantially elongate, and is disposed in channel 33 having a substantially semi-circular cross-sectional profile. In one embodiment, channel 33 extends from slot wall 37 through dovetail slot 32. Load pin 34 secures each nozzle assembly 28 to stator 22.

[0021]FIG. 3 is an enlarged cross-sectional side view of load pin 34 used in the turbine nozzle assembly 28 shown in FIG. 2. FIG. 4 is an end view of load pin 34 shown in FIG. 3. Load pin 34 includes a first end 100, a second end 102, and a body 104 extending therebetween. Load pin 34 has a substantially semi-circular cross-sectional profile that includes a substantially circular portion 106 with a center point 107 and a radius 108, and a substantially straight portion 110. Load pin 34 further includes a length 112 and a height 114. In the exemplary embodiment, radius 108 is approximately 0.158, length 112 is approximately 0.920, and height 114 is approximately 0.200. In one embodiment, radius 108 is approximately between 0.157 and 0.159, length 112 is approximately between 0.915 and 0.925, and height 114 is approximately between 0.198 and 0.202. In another embodiment, radius 108 is approximately between 0.153 and 0.163, length 112 is approximately between 0.910 and 0.930, and height 114 is approximately between 0.195 and 0.205. In the exemplary embodiment, load pin 34 is fabricated from brass. In another embodiment, load pin 34 is fabricated from bronze. In an alternate embodiment, load pin 34 is fabricated from steel.

[0022] The above-described stator assembly is efficient and cost-effective device. The stator assembly includes a radial load pin that facilitates securing a nozzle assembly to the stator assembly, thus reducing the chances of unpredictable flow path dynamics. Furthermore, the radial load pin is inexpensive and easy to manufacture. As a result, the radial load pin facilitates stabilizing flow path dynamics in an efficient and cost-effective manner.

[0023] Exemplary embodiments of stator and nozzle assemblies are described above in detail. The systems are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. Each stator and nozzle assembly component can also be used in combination with other stator and nozzle assemblies and turbine components.

[0024] While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims. 

1. A method for assembling a turbine, said method comprising: coupling at least one nozzle assembly including an outer band, an inner band, a nozzle, and a dovetail, to a stator that includes a plurality of dovetail slots and channels defined therein; slidably coupling the at least one nozzle assembly into a respective dovetail slot; and fixedly securing the at least one nozzle assembly to the stator with a load pin that extends between the nozzle assembly and the dovetail slot.
 2. A method in accordance with claim 1 further comprising forming a channel that extends at least partially through the stator dovetail slot and is sized to receive a load pin therein.
 3. A method in accordance with claim 1 wherein fixedly securing the at least one nozzle assembly to the stator comprises inserting the load pin through the stator channel.
 4. A method in accordance with claim 1 further comprising forming a plurality of channels that each extend at least partially through the stator dovetail slot, and are sized to receive at least one load pin therein.
 5. A method in accordance with claim 1 wherein fixedly securing the at least one nozzle assembly further comprises fixedly securing the at least one nozzle assembly to the stator using at least one load pin that has a substantially semi-circular cross-sectional shape.
 6. A method in accordance with claim 1 wherein fixedly securing the at least one nozzle assembly further comprises fixedly securing the at least one nozzle assembly to the stator using at least one load pin fabricated from at least one of a brass, a bronze, and a steel material.
 7. A stator assembly for a turbine, said stator assembly comprising: a stator comprising a plurality of dovetail slots and channels; at least one nozzle assembly secured to said stator, said at least one nozzle assembly comprising an outer band, an inner band, a nozzle, and a dovetail, said nozzle extending radially outwardly from each said dovetail; and at least one load pin for securing said at least one nozzle assembly to said stator such that said load pin extends between said at least one nozzle assembly dovetail and said at least one stator dovetail slot.
 8. A stator assembly in accordance with claim 7 wherein said at least one load pin comprises a substantially semi-circular cross-sectional profile.
 9. A stator assembly in accordance with claim 7 wherein said at least one load pin comprises at least one of a brass, a bronze, and a steel material.
 10. A stator assembly in accordance with claim 7 wherein said at least one load pin extends through a portion of said stator dovetail slot.
 11. A stator assembly in accordance with claim 7 wherein said at least one load pin extends through a portion of said stator channel.
 12. A stator assembly in accordance with claim 7 wherein said at least one load pin further comprises an upstream load pin and a downstream load pin.
 13. A turbine comprising: at least one rotor assembly; at least one stator assembly in flow communication with said at least one rotor assembly, said at least one stator assembly comprising a stator comprising a plurality of dovetail slots and channels; at least one nozzle assembly secured to said stator, said at least one nozzle assembly comprising an upstream side, a downstream side, a vane and a dovetail, said vane extending radially from said dovetail; and at least one load pin for securing said at least one nozzle assembly to said stator such that said load pin extends between said nozzle assembly dovetail and said stator dovetail slot.
 14. A turbine in accordance with claim 13 wherein said at least one load pin comprises a substantially semi-circular cross-sectional profile.
 15. A turbine in accordance with claim 13 wherein said at least one load pin comprises at least one of a brass, a bronze, and a steel material.
 16. A turbine in accordance with claim 13 wherein said at least one load pin extends through a portion of said stator channel.
 17. A turbine in accordance with claim 13 wherein said at least one load pin extends through a portion of said stator dovetail slot.
 18. A turbine in accordance with claim 13 wherein said at least one load pin further comprises an upstream load pin and a downstream load pin. 